Incandescent lamp with tac filament and cyanide-radical producing and halogen atmosphere



Oct. 4, 1966 D. P. COOPER, JR 3,

INCANDESCENT LAMP WITH TaC FILAMENT AND CYANIDE-RADICAL PRODUCING AND HALOGEN ATMOSPHERE Filed July 15, 1960 TANTALUM CARBIDE FlLAMENT CYANlDE-RADICAL PRODUCING AND l6 HALOGEN ATMOSPHERE INVENTO M/QW,

United States Patent 3,277,330 INCANDESCENT LAMP WITH TaC FILAMENT AND CYANIDE-RADICAL PRODUCING AND HALOGEN ATMOSPHERE Dexter P. Cooper, Jr., Lexington, Mass., assignor to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware Filed July 15, 1960, Ser. No. 43,054 The portion of the term of the patent subsequent to Feb. 20, 1979, has been disclaimed 5 Claims. (Cl. 313-474) This application is a continuation-in-part of my copending application Serial No. 840,495, filed September 10, 1959, now US. Patent No. 3,022,438, issued February 20, 1962, which in turn is a continuation-in-part of my application Serial No. 559,394, filed January 16, 1956 and now abandoned.

This invention relates to new and improved electric incandescent lamps adapted to be operated at relatively high filament temperatures and possessing relatively long, useful operating life at such high temperatures.

Objects of the invention are to provide incandescent lamps of the character described in which the filament comprises tantalum carbide and in which the envelope of the lamp contains an atmosphere comprising at least one source of carbon and at least one source of nitrogen.

Another object of the invention is to provide an incandescent lamp of the above type wherein the atmosphere also includes at least one source of at least one halogen.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the product possessing the features, properties, and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will .beindicatedinthe claims.

For a fuller understanding of the nature and objects of the inventiomreference should be had to the follow-, ing detailed description taken in connection with the accompanying drawing, which is a representation of a sec ice is positioned within an atmosphere 12 comprising, at operating temperatures, at least nitrogen and carbon. The atmosphere. may also include at least one halogen. An inert gas of low heat conductivity such as argon may also be included in the atmosphere.

The components of the atmosphere may be provided by introducing one or more suitable materials as hereinafter mentioned before the bulb is sealed. The filament 10 may be suspended between leads 14, which are in turn attached to subleads 16; the subleads may be connected to a source of electric power outside the envelope 18. If the invention is to be used in vehicle headlamps of the sealed beam type as illustrated, the inner cupshaped surface 20 is silvered, aluminized, or otherwise coated to provide a reflecting surface. The bulb and components may be cleaned and prepared in ways well known to the art. When the atmosphere includes a halogen, e.g., fluorine, it is often desirable to coat the inner surfaces of the envelope (preferably after formation of the reflector, if such is used) with a material that will 7 protect the envelope material, e.g., glass, from attack.

tion through a typical automobile headlamp embodying the features of the invention.

Present-day electric incandescentlamps are generally constructed with a tungsten filament mounted in an evacuated atmosphere within the bulb or in an atmosphere comprising essentially inert gases. These inert gases may, for example, comprise a mixture of gases of which the major portion is argon, krypton or xenon. Inert gases are employed to reduce evaporation of the filament during lamp operation. Nevertheless, a common cause of lamp failure is evaporation of filament material to such an extent that the filament is gradually eaten away and fails. Since the rate of evaporation varies directly with the temperature, this kind of failure is especially prevalent in bulbs designed to operate at very high temperatures. Rapid filament evaporation has long been a serious problem in incandescent lamp manufacture,

since the efficiency of the bulb as a source of illumination, measured in candle power per watt, for example, generally increases as the operating temperature of the filament is raised.

This invention accordingly contemplates the use of an atmosphere the elements of which interact with each other and with a tantalum carbide filament in such a inanner that the filament does not deteriorate over an extended period of operation at high filament temperatures. The invention thus yields a lamp that has both long operating life and high efliciency.

In one embodiment of this invention, shown in one application in the drawing, a tantalum carbide filament This may be done by evaporating calcium fluoride, for example, upon the inner surfaces of the envelope before the lamp is completely assembled.

The filament may be of any suitable configuration, whether straight, coiled, crimped, or otherwise shaped. Although any convenient method of forming a tantalum carbide filament or leads may be used, it may be convenient, for example, to convert a tantalum filament and tantalum leads (if used) to tantalum carbide after the bulb has been assembled. For example, the bulb may be constructed such that the filament and leads may comprise essentially pure tantalum. In the presence of a carburizing atmosphere, e.g., a volatile hydrocarbon and hydrogen, the filament may then be converted to tantalum carbide by passing sufficient current through the filament to yield a filament temperature of about 3100 C. and

" maintaining the filament at such temperature for a suitable length of time. In this way, the filament and lead ends associated with it will be substantially converted to tantalum carbide. The carburization of a tantalum filament may be accomplished in situ by the active envelope filling also employed for operation or the filament may be carburized previously in a carburizing atmosphere other than that employed for operation.

Many materials may be used for the leads. For ex filament or they may be rods made of carbon, nickel, tungsten, platinum, palladium, rhodium, molybdenum or suitable metals coated or plated with platinum, palladium, rhodium and the like.

In the following representative tabulated runs, various size envelopes comprising a light-transmissive material such as glass were employed. A filament comprising tantalum carbide was supported upon suitable leads within the envelope. The tantalum carbide filament was prepared either by carburization of a tantalum filament in situ by the operating atmosphere or preformed by heating a tantalum filament to very high temperatures in the presence of an atmosphere such as methane, ethylene or the like and hydrogen. In general, prior to introducing the material or materials from which the operating atmospheres were derived, the bulb envelopes were evacuated to remove deleterious gases such as oxygen.

In Table I there is illustrated a number of typical runs in which all the desired components or elements of the envelope atmosphere are derived, at least in part, from amines such as methylamine hydrochloride, etc.

TABLE I Envelope Filling Life, Hours at Bulb K. Color Size, Temperacc. ture, K. Carbon-Nitrogen Containing Compound Nitrogen Hydrogen, Argon Aver- Maxice. age mum 20 cc. cyanogen To atmospheric pressure.. 3, 500 Dicyandiamide. ..do 3 500 Do 3,600 4 cc. hydrogen cyani c...-- 3, 400 cc. hydrogen cyanide 3, 400 20 co. hydrogen cyanide...-. 3, 400 17.3 cc. hydrogen cyanide 833 cc 3 400 20 cc. hydrogen cyanide 770 cc. 3, 400 23 cc. hydrogen cyanide. 770 cc- 3, 400 20 cc. hydrogen cyanide- 833 cc- 3, 400 11.2 cc. hydrogen cyanide 833 cc 3, 400 cc. hydrogen cyanide 833 cc 3, 400 17 .6 cc. hydrogen cyanide.. 625 ccg, 22 cc. hydrogen cyanide To atmospheric pressure.. 2, :08

0 y 8 mg. methyl-amine hydrochloride. About 38 cc. 3, 400 10 rug. methylamine hydrochloride About 42 cc 3, 400 12 mg. methylamine hydrochloride About 67 cc. 1 3, 315 17 mg. methylamine hydrochloride About 56 cc 1 3, 470 20 mg. methylamine hydrochloride About 58 cc 1 3, 470 mg. Inethylamine hydrochloride 3, 000 10-20 mg. ethylenediarnine dihydroohl ride. About cc 3, 400 Ethylenediamine dihydrochloride About 135 cc. 3, 400 Succinonitrile. l 3, 430 Adiponitrile 3, 590 Glutaronitrile 1 3, 460 Succinonitrile. About atmos 1 3, 570

Average.

Envelope fillings other than those set forth above have been tried and found operative.

For example, fillings or bulb atmospheres.

Moreover, ratios of envelope elements or components other than those shown by way of ex- 30 I conslstmg a.cyamde Iadlcal coniammg compound Such ample only in Table I have been found to give useful lives. as cyanarnide 1n the presence of nitrogen or nitrogen and In Table II, there is illustrated a number of typical hydrogen, cyanogen the Presence of argon or nitrogen runs in Which the desired envelo e co t d and hydrogen, and acetonitrile in combinatlon with mtrorived from lur n t of at 1 p mponen S are 6 gen have also been found to provide operative envelope a p a y m ena TABLE II Envelope Filling Life, Hours at Bulb K. Color Size, Temp, cc. K. Carbon-Containing Hydro- Other Nitrogen Argon Avg. Maxi- Compound gen, cc. mum

4 cc. propane V To produce 1.0 inch 1, 000 16.0 3, 400 total pressure.

1, 000 58. 5 3, 025 5 cc, methane 4.0 11101195 1, 000 25. 5 16. O 3, 230 1, 000 2.0 3, 550 I 1, 000 9. 0 3, 475 30 cc. methane 100 To produce 4.0 inches 1,000 48 0 2. 0 3, 500 total pressure. 1, 000 171. 0 3, 400 1, 000 9. 0 3, 440 Do 400 5.0 11101198-. 1, 000 2.0 3, 400 1, 000 13. 5 3, 400 5 co. methane 22 973 oi 22. 0 g i 1, 000 42. 0 31400 50 methane cc. ammonia- To produce 5.0 inches 1,000 130.0 3, 400 total pressure. Do Ammonia to produce 5.0 1, 000 72, 0 I 3 1 inches total pressure. 2 cc. butane 15 Ammonia to produce About atmosphere. 250 3.83 6. 5 3, 400

about atmosphere. .15 cc. acetylene 100 cc. ammonia. To produce 4.0 inches 1, 000 18. 5 3, 400 total pressure. Do Ammonia to produce To produce 10.0 1, 000 24. 0 3, 400

about atmosphere. inches total pressure. 7 cc. methyl chloride- 0 produce 1.0 inch 1, 000 3. 8 5. 0 3 400 total pressure. 25 cc. methyl chloride. To produce 4.0 inches 1, 000 4, 5 1 3 total pressure. 25 c methane 100 Iodine To about atmospheric 1,000 24. 0 3, 400

pressure. Do 100 5 cc. hydrogen bromide. .do- 1, 000 40.0 3, 400 Do 100 510gcc. hydrogen chlo- .do- 1, 000 2. 0 3, 400

11 e. 2% ethylene- 0.24 gram ammonium 70 5. 0 3 400 chloride. 2.5 cc. butane 17. 5 2.5 cc. chlorine To produce about 16 About }4 atmosphere... 250 4. 7 7. 0 3, 400

atmosphere pressure. Do. 17.5 -.do To produce about 34 About atmosphere-- 250 4. 8 5. 66 3, 400

atmosphere pressure. 0,25 cc. butane 5 4 co. hydrogen chloride-... To produce about 36 About atmosphere" 250 4. 5 a, 500

atmosphere pressure. 5 cc. hydrogen chloride 15 cc- 250 11. 0 3, 500 5 ....d0. 7 15 cc. 250 23. 25 3, 500 2.5 cc. hydrogen chloride.-- 5 cc- 250 9. 25 13.25 3, 500 5 cc. hydrogen chloride.... 15 co- 250 13.0 19. 66 3, 500

1 Average.

Ratios of envelope elements or components other than those given above by way of example only in Table II have been found to provide operative atmospheres.

At operating temperatures, the gaseous atmospheres provided by the envelope fillings listed in the tables, particularly in the vicinity of the incandescent filament, continuously undergo a number of reactions, such as decomposition and recombination to provide, during operation, an active carbonaceous blanket around the filament which prevents the rapid loss of carbon from the filament. In other words, an equilibrium is established between the filament comprising tantalum carbide and the gaseous carbon-containing atmosphere surrounding the filament. The various envelope fillings set forth in the tables undergo reaction during lamp operation to provide partial pressures of cyanide-containing gases, unsaturated hydrocarbons and the like. Thus, envelope fillings containing hydrocarbons such as, for example, methane, propane, butane, methyl chloride and the like in combination with nitrogen produce, among other products, hydrogen cyanide during opperation. Partial pressures of cyanide-containing gases are also obtained when envelope fillings comprising, for example, acetylene and ammonium or amide-s such as methylamine hydrochloride etc. are employed. For example, the contents of a bulb initially filled with methane, hydrogen and nitrogen were analyzed during operation and found to contain appreciable quantities of hydrogen cyanide. A lamp filled with 20% nitrogen, 2.0% hydrogen and 0.64% carbon tetrachloride and run for five minutes at 3500 K. indicated the presence of 0.033% acetylene, 0.55% hydrogen cyanide and hydrogen chloride. A lamp filled with 1.0% nitrogen, 2% hydrogen and 0.8% carbon tetrachloride and run for 5 minutes at 3500 K. indicated the presence of 0.046% acetylene and 0.118% hydrogen cyanide. The carbon-containing components of the atmosphere such as hydrogen cyanide undergo decomposition when in very close proximity to the incandescent filament to provide the desired carbonaceous blanket therearound.

The desired atmospheres may be provided by a number of materials or sources. For example, suitable lamp atmospheres may be provided by cyanogen or a combination of cyanogen and nitrogen and/ or hydrogen. Suitable lamp atmospheres may also be provided by including a halogen such as chlorine, or hydrogen halide or the like with materials of the above-mentioned type or by providing a combination of a halogenated hydrocarbon, e.g., methyl chloride, benzene hexachloride, carbon tetrachloride and the like, and nitrogen. Cyanogen halides such as cyanogen chloride, iodide, bromide and fluoride may also be employed. In addition to cyanogen, other cyahide-radical containing materials such as cyanamide, dicyandiamide, hydrogen cyanide and the like may also be employed. The atmosphere may likewise be provided by a combination of nitrogen and a hydrocarbon such as methane, ethane, propane, butane, ethylene, acetylene and the like. A combination of ammonia and a hydrocarbon such as methane, acetylene, etc. is also satisfactory. Various derivatives of ammonia, for example amines and nitriles, may also be used to provide a source of nitrogen and carbon. For instance, there may be employed amines such as methylamine, aniline, toluidine, polyamines such as ethylenediamine, hexamethylenetetramine, etc., and nitriles such as adiponitrile, glutaronitrile, succinonitrile, acetonitrile and the like. Hydrazine and derivatives there of, e.g., phenylhydrazine may be used in combination with a carbonaceous material to provide the desired atmosphere. A combination of a cyanide-radical containing material as cyanamide, with a halogen or hydrogen halide gas, may also be employed. Combinations of nitrogen or nitrogen and hydrogen with a hydrocarbon such as methane, butane, etc., and a halogen, e.g., chlorine, iodine, etc., or hydrogen halide, e.g., hydrogen chloride, are also satisfactory. Mixtures of an ammonium halide, e.g., ammonium chloride and a hydrocarbon, e.g., ethylene, may also be employed. These atmospheres may also be provided from single materials, for example, the quaternary ammonium salts such as tetramethylammonium iodide, or the hydrogen halide salts of amines and polyamines such as methylamine hydrochloride, ethylenediamine dihydrochloride, and the like. It is obvious that the desired atmospheres thus may be obtained in any number of suitable ways. Inert gases of low heat conductivity, such as an argon, xenon and krypton, may also be included in the lamp atmospheres.

Relatively high pressures within the bulb will lengthen lamp life; it is desirable to maintain the pressure during operation at or near the highest level that the envelope can safely withstand. If the pressure generated by the reacting gases is great enough, the need for an inert gas is reduced.

The halogens, in general, that is, chlorine, bromine, iodine and fluorine,.may be included within the lamp atmosphere as indicated above. If fluorine is used, however, precau-tions must be taken to avoid decomposition of the bulb envelope and attack upon other lamp elements. If elemental halogens are used in preparing the lamp atmosphere, precautions should be taken to avoid inhalation or contact with skin and eyes.

In general, any combination of materials may be used that will provide an atmosphere comprising at least carbon and nitrogen in the area surrounding the filament. It may also include at least one halogen. The atmosphere should be substantially free of water or oxygen. The

amount of carbon in the atmosphere should be sufficient to prevent the tantalum carbide filament from decomposing into free tantalum and carbon. The other components, such as nitrogen and halogen, may be used in varying proportions; the total amount of these components should, however, be sufiicient to combine with carbon atoms escaping from the region surrounding the filament -to reduce to a minimum the deposit of uncombined carbon upon the inner wall of the bulb or upon other exposed surfaces. As may be seen from the tables, a wide range of partial pressures of nitrogen and other active gases may be employed. For example, partial pressures of nitrogen ranging from but a few tenths of a centimeter to almost 76 centimeters of mercury may be satisfactorily employed. Likewise, as may be seen from the tables, partial pressures of active gases such as the cyanide-radical containing gases may extend over a wide range of millimeters of mercury. For example, in the hydrogen cyanide runs reported in Table I, partial pressures thereof are shown as being between about 3 and 17.5 millimeters of mercury times the reciprocal of the number of (CN) radicals present in the molecular formula of hydrogen cyanide. In these runs the nitrogen partial pressures are at least 47.5 centimeters of mercury.

While the drawing particularly illustrates the applicability of the present invention to vehicle lamps, it is understood that the invention may be advantageously employed generally with incandescent lamps, for example photoflood lamps, projection lamps, and other structures adapted to project carefully controlled or substantially collimated light beams.

Moreover, while the drawing describes a specific lamp configuration or structure, it is understood that the incandescent lamp may take any desired shape and have any desired size. It may, for example, have an envelope which is either transparent or translucent in whole or in part, and, where a portion only of the envelope is light transmitting, the remainder may comprise a parabolic or other suitable reflector with the lamp filament positioned at the focus thereof.

Since certain changes may be made in the above products without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An incandescent lamp comprising an evacuable lighttransmissive envelope having therein a filament or tantalum carbide and a gaseous filling containing halogen and which upon thermal decomposition produces a partial pressure of cyanide radical containing gas in the vicinity of said filament when said filament becomes incandescent.

2. The incandescent lamp of claim 1 wherein the halogen is chlorine.

3. The incandescent lamp of claim 1 wherein the halogen is bromine.

4. The incandescent lamp of claim 1 wherein the halogen is iodine.

5. The incandescent lamp of claim 1 wherein the gaseous filling contains hydrogen.

References Cited by the Examiner UNITED STATES PATENTS 674,754 5/ 1901 Blau 3162 2,072,788 3/1937 Andrews 313 -179 2,928,977 3/1960 Roth et al 313-222 0 JAMES W. LAWRENCE, Primary Examiner.

RALPH G. NILSON, DAVID J. GALVIN, GEORGE N. WESTBY, Examiners.

15 R. SEGAL, V. LAFRANCHI, Assistant Examiners. 

1. AN INCANDESCENT LAMP COMPRISING AN EVACUABLE LIGHTTRANSMISSIVE ENVELOPE HAVING THEREIN A FILAMENT OR TANTALUM CARBIDE AND A GASEOUS FILLING CONTAINING HALOGEN AND WHICH UPON THERMAL DECOMPOSITION PRODUCES A PARTIAL PRESSURE TO CYANIDE RADICAL CONTAINING GAS IN THE VICINITY OF SAID FILAMENT WHEN SAID FILAMENT BECOMES INCANDESCENT. 